Environmentally friendly fluids comprise mainly vegetable oils. Vegetable oils have a low viscosity and therefore tend to flow off surfaces providing poor film forming and thus giving poor lubrication.
In order to "body up" the vegetable oils a polymeric viscosity improver is utilized. The problem is in finding a viscosity improver that is soluble in vegetable oils.
U.S. Pat. No. 4,391,721 (Pappas, Jul. 5, 1983) relates to dispersant viscosity index improvers that comprise the reaction product of an aliphatic alcohol or mixtures thereof, a tertiary amino alcohol and a styrene maleic anhydride copolymer. The lubricating oil additives of this invention are prepared by first copolymerizing styrene and maleic anhydride, reacting the copolymer with a C.sub.6 or greater aliphatic alcohol or mixture of aliphatic alcohols until the copolymer is substantially completely esterified and then transesterifying with a tertiary amino alcohol. By transesterifying, the inventor means displacing the aliphatic alcohol from a fraction of the ester groups and replacing them in the ester with a tertiary amino alcohol.
U.S. Pat. Nos. 4,970,011 and 5,094,764 (Kuwamoto et al, Nov. 13, 1990 and Mar. 10, 1992) relate to a lubricating oil composition containing as essential ingredients a lubricating oil component having a melting point of not higher than 100.degree. C., and one or more water-soluble dispersants selected from the group consisting of anionic polymeric dispersants of a molecular weight of 250 to 25,000, and polyoxyethylene type surfactants of a molecular weight of 3,000 to 20,000 and an HLB value of at least 18, said lubricating oil component being present in a stably dispersed state in water, achieves excellent adhesion when supplied to a machined portion.
U.S. Pat. No. 3,702,300 (Coleman, Nov. 7, 1972) relates to a carboxy-containing interpolymer in which some of the carboxy radicals are esterified and the remaining carboxy radicals are neutralized by reaction with a polyamino compound having one primary or secondary amino group which is useful as an additive in lubricating compositions and fuels. The interpolymer is especially effective to impart desirable viscosity characteristics and anti-sludge properties to a lubricating oil.